Wednesday, November 15, 2006

Ruminal Degradation of Specific Alfalfa Proteins.

Michael Peel1, Dong Chen2, Kenneth C. Olson2, Daryll B. DeWald2, and Bart C. Weimer2. (1) USDA-ARS Forage & Range Research La, 695 North 1100 East, Logan, UT 84322-6300, (2) Utah State University, 4700 Old Main Hill, Logan, UT 84322

Alfalfa has one of the highest crude protein contents among forages but the crude protein is rapidly and extensively degraded in the rumen.  Our objectives were to i) identify the major specific proteins in alfalfa, and ii) quantify the rate of ruminal degradation of those major proteins after 0, 45 and 120 min digestion in the rumen.  Proteins from single plants of three alfalfa’s were labeled with different fluorescent dyes for each of the time points and separated on single 2D gels.  Gels were scanned for fluorescence representing quantities of the individual proteins from the time points.  Twenty six individual proteins were characterized, they represented on average 36% of total protein detected.  Significant variation for rate of protein degradation was observed for germplasm source and for proteins after 45 and 120 m (P=0.003). The digestion rate for some proteins differed (P=0.05) among plants.  After 45 m nine proteins averaged 75% or more remaining, 12 had 50% or less remaining, and six were intermediate.  After 120 m four proteins averaged greater than 80% remaining, seven between 80 and 50%, and 16 less than 50% remaining.  Generally proteins were uniformly more digested with increasing time, however, differences in disappearance became more pronounced with time.  The rate of digestion differed for two and 10 proteins among genotypes after 45 and 120 m respectively.  Of the protein content characterized individual proteins as a percent of the total ranged from 41% (large subunit of RUBISCO) to 0.29 % (Malate dehydrogenase precursor).  Total content of individual proteins that differed for digestion rate among genotypes ranged from 7 to 1%. The results suggest variability among individual proteins and the potential to develop alfalfa with more protein that degrades slowly in the rumen and possibly escapes degradation in the rumen.